Both Chinese and American Indian populations are exposed to high levels of complex, environmental PAH mixtures and lung cancer mortality rates have increased in both populations in recent years. The complex PAH mixtures these populations are exposed to remain poorly characterized and this is a major limitation in risk assessment. Due to the rapid increase in coal-fired power plants, China is the largest, and exponentially growing, emitter of mutagenic, particulate matter (PM)-bound polycyclic aromatic hydrocarbons (PAHs) in the world. The issue extends beyond local exposure because trans-Pacific atmospheric transport of these PAHs to the U.S. occurs in as little as 5 days. We hypothesize that 1) Chinese and American Indian populations are exposed to high concentrations of different complex environmental PAH mixtures;2) nitro and oxy-PAHs are formed on Asian PM in transit to the U.S.;and 3) Asian PM results in a measurable increase in the mutagenicity of PM in the western U.S. Our monitoring of trans-Pacific transport offers a unique opportunity to test these hypotheses on a global scale. Our first specific aim will measure the PMbound PAH composition and exposure to nonsmoking Chinese in the Beijing-Tianjin metropolitan area and American Indian men and women on the Confederated Tribes of the Umatilla Indian Reservation (CTUIR) using personal air sampling and novel assays of urinary metabolites. Our second specific aim will measure the aging of Asian PM in situ in the atmosphere and in the laboratory. This will be accomplished using a series of monitoring sites from Beijing, China to Okinawa, Japan to Mt. Bachelor and Portland, Oregon and the CTUIR and comparing the results to simulated atmospheric aging in a laboratory reactor. Such studies have never been conducted before. Our third specific aim will measure the mutagenicity of the different types of PM collected and link this information to Chinese and American Indian PAH exposure. These data will be of great value for improving estimates of the human health impact of PAHs on highly exposed populations. Novel urinary metabolites will be investigated in collaboration with Cores C and D and air mass trajectories and measurements will be incorporated into a web-based GIS platform that will be used by state and federal agencies in collaboration with Core B. American Indian tribal capacity will be strengthened by transferring air sampling technology to and training tribal members in collaboration with Core E.